1. Field of the Invention
The invention relates to a power converter device, more particularly, an AC-to-DC converter device.
2. Description of the Related Art
With the electronic devices, such as home appliances, having intelligent features gaining great popularity, the use of standby power becomes an important topic. Standby power is the power needed when an electronic device is on standby (or, in idle) such as for maintaining a designated mode of operation, decreasing start up time, or waiting for a remote command. Standby power is different from main power needed for normal operation of the electronic device. The voltage level of standby power is usually substantially less than that of main power and needs to be generated separately.
FIGS. 1 and 2 show a conventional design of an offline AC-to-DC power converter 1 usually seen in electronic devices. The offline AC-to-DC power converter 1 includes an AC-to-DC power converter circuit 11, a step-down DC converter circuit 12, a standby power converter circuit 13 and a pulse-width modulation (PWM) signal generator 14. The AC-to-DC power converter circuit 11 converts an AC input voltage (90-264 Vac) into a DC bus voltage (VBUS) (380V). The step-down DC converter circuit 12 then performs a step-down conversion on the DC bus voltage (VBUS) so as to output a main voltage (VDC). The standby power converter circuit 13 performs a step-down conversion on the DC bus voltage (VBUS) so as to output a standby voltage (Vsb). The PWM signal generator 14 generates two PWM signals opposite in phase to respectively perform switching on a first switch (SW1) and a second switch (SW2) of the step-down DC converter circuit 12. When the electronic device operates in a normal mode, the step-down DC converter circuit 12 provides the main voltage (VDC) for operation. When the electronic device operates in a standby mode, the standby power converter circuit 13 provides the standby voltage (Vsb) for operation.
However, when the main voltage (VDC) and the standby voltage (Vsb) are both needed in the normal mode, the following happens. The standby power converter circuit 13 is an isolation type flyback converter circuit that receives the DC bus voltage (VBUS) and outputs the standby voltage (Vsb) and thus operates under high input/output potential difference. The load (hence the resistance) is substantially larger in the normal mode than in the standby mode. Where a large output is required under a large load, the presence of leakage inductance and distributed capacitance (from stray or parasitic components) will increase voltage and current surges, causing conversion loss, which becomes more evident as the load increases, and decreasing the stability of power provision.